String safeChars = "\0\u0100\uD800\uDC00\uFFFF";
    assertEquals(safeChars, escaper.escape(safeChars));

    // Ensure that Unicode escapers behave correctly wrt badly formed input.
    String badUnicode = "\uDC00\uD800";
    try {
      escaper.escape(badUnicode);
      fail("should fail for bad Unicode");
    } catch (IllegalArgumentException e) {
      // Pass
    }
  }

    String safeChars = "\0\u0100\uD800\uDC00\uFFFF";
    assertEquals(safeChars, escaper.escape(safeChars));

    // Ensure that Unicode escapers behave correctly wrt badly formed input.
    String badUnicode = "\uDC00\uD800";
    try {
      escaper.escape(badUnicode);
      fail("should fail for bad Unicode");
    } catch (IllegalArgumentException e) {
      // Pass
    }
  }